Add support for server-side paging

[deveiant]

Add a high-level implementation of the  Simple Paged Results control via the controls API added in #2.

This will either be a separate 'Pager' class that will provide methods for fetching pages from the server given a page size, offset, and source Treequel::Branchset, or a set of methods for doing the same added directly to Treequel::Branchset as part of its enumerable interface.

dir = Treequel.directory

people = dir.ou( :people ).
    filter( :objectClass => :inetOrgPerson ).
    order( :sn, :givenName, :uid ).
    pagesize( 25 )

people.pages.each do |page|
    page.each do |person|
        puts "%s, %s <%s> (%d)" %
            person.values_at( :sn, :givenName, :mail, :uidNumber )
    end
    unless page.last?
        puts "Page %d/%d. Continue? [Y/n]" % [ page.current, page.max ]
        answer = $stdin.gets
        break unless answer =~ /^y/i
    end
end

[deveiant]

Committed in r244.